Mechanical calculators: FACIT ESA-0

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This machine was manufactured by FACIT in Sweden, in 1951 (see here). I bought it at an online auction site, in April 2019, right after finding my NEA. As in that case, there was no way of knowing if the motor would run, since the seller only said it was completely jammed, and that he didn't have the power cable. In spite of three missing keys, I bought it anyway, for three times the price I paid for the NEA. The exterior was very attractive, displays were all zeroed, and the ADD key was slightly lower than its reset position, so I guessed the jam would be related to that.

This machine evolved from the NEA, adding an automatic multiplying function, that also works for squaring. The division works exactly in the same way as in the NEA, also automatically. Thus, this model was the first FACIT to be fully automatic for the four operations. The initial ESA kept the manual reset levers to the right, but soon evolved into the ESA-0, with electrically-operated clearing mechanisms for all three registers.

My machine has octogonal keytops for the shift functions, and a knurled lever for the stop/sub function. This lever was replaced with a regular button in later models, and the TK-style octogonal keytops also evolved into rectangular ones.

My machine also lacks the secondary control lever, to the right of the main control (mult-add-div) lever. This is strange, since the NEA has this lever, and its bottom prints symbols to indicate its function to the operator. Most other pictures of ESA-0 machines I found online also have the secondary lever. This site indicates that the first 10,000 units of this model did not have that lever. In the NEA and in the CS1-13, the lever is used to activate or deactivate the carriage shift to the left when using the manual multiplication mode (using the big + key instead of the X and = keys, which are missing in the NEA and the CS1-13). Since the ESA-0 offers automatic multiplication, this lever seems unnecessary, except maybe for the sake of backward compatibility with the simpler models.

Putting it back to work was a demanding process, since initially the motor ran continuously, and all other mechanisms were locked, including the keyboard and main rotor. It took some analysis, observation, kerosene jets and lubrication to unlock the typical parts of the FACITs that cause the most important locks. During two careful days, I made it a new power cable, then I managed to stop the ever-running motor, make the clearing mechanisms work, unlock the main rotor, release the keyboard lock, activate the adding mechanism, and finally get it to do multiplications and divisions. It now works perfectly.

I replaced the acetate windows, cutting from a transparent sheet that is used in packing kiwi fruits for sale in Brazil – go figure. I have also replaced the rubber rollers at the back with nylon cylinders. At 12 kilos, this was the first FACIT machine to have rollers to help moving it around an office desk. Next step: 3D print the missing keytops (done in 2020, see below).

Multiplication in the ESA-0 is straightforward: the operator types in the multiplicator, and presses the X button. This places the multiplicator in a “mechanical memory” of sorts, the input register is cleared, and the displays remains zeroed. Then the operator inputs the multiplicand, and presses the = key. The result comes out automatically, with all rotations and shifts performed automatically. It is worth mentioning that the mechanical algorithm implemented in this machine can optimize the number of rotor turns, deciding whether to go forward or backwards so that the number of turns is minimized.

The operator can help minimizing the machine's effort. As a rule, enter first the smaller number. If the numbers have the same number of digits, there can be a more efficient multiplication order. For instance, if the operator enters 333 x 999 =, the machine stores 333, then spins the rotor with 999 in the input register three times, for each of the three decimal positions, so nine turns are required. If the operator enters 999 x 333 =, then 999 is stored, and with 333 in the main rotor, the machine performs one negative turn (-1 x 333), then shifts left three times, then does one positive turn (+1000 x 333), and completes the task with only three spins.

Division is also fully automatic: after the dividend is input and added to the left of the accumulator, the input register is cleared automatically and the divisor can be keyed in and also shifted to the left. Then the division key starts up a mechanical algorithm by which subtractions and carriage moves to the right go on automatically until the remainder is zero or the precision limit is reached.

Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!

1951 FACIT ESA-0 s/n 327930

Front view, notice there is no secondary control lever to the right of the main lever

 Front view

Left side, cover off

 Left side

Right side, cover off

 Right side

Motor, by Electrolux, another Swedish company that decades later acquired FACIT


Electrical connections in the motor shaft

 Electrical connections

Front view, still missing three keytops

 Still missing three keytops

Power label at the back. I adapted a Brazilian 20A connector to fit the thick prongs used back then

 Power label in the back

Bottom panel, after treating some rust and replacing the rollers with nylon cylinders

 Bottom panel

3D printed replacement buttons

 Bottom panel

As purchased

 As purchased

More about this machine

The evolution of FACIT calculators

Video: a demonstration of the FACIT ESA-0 features and use modes

Manual of the FACIT CA1-13 (in German), similar to the ESA-0 except for the cover, and the separation of the SUB/STOP lever functions into two keys. For some reason, FACIT inverted the numbering of the input and accumulator registers, but not the position of the keys

Another description of the CA1-13, in English, mostly applicable to the ESA-0

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facit_esa-0.txt · Last modified: 2021/10/17 14:23 by clodoveu
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